Some Multiple-Input Multiple-Output (MIMO) communication systems use cooperative transmission schemes, in which multiple base stations coordinate beamforming and precoding decisions with one another. Coordinated transmission is also referred to as coordinated beamforming or Coordinated Multipoint (CoMP). Coordinated transmission is considered, for example, for Evolved Universal Terrestrial Radio Access (E-UTRA) systems, also referred to as Long-Term Evolution (LTE), which are specified by the Third Generation Partnership Project (3GPP). Cooperative beamforming for LTE is described, for example, in document R1-093488 of the 3GPP Technical Specification Group (TSG) Radio Access Network (RAN), entitled “LTE Spectral Efficiency and IMT-Advanced Requirements,” Shenzhen, China, Aug. 24-28, 2009, which is incorporated herein by reference.
Coordinated transmission schemes often use feedback regarding the communication channels, which is fed back from the mobile terminals to the base stations. An example feedback scheme for coordinated transmission is described in 3GPP TSG RAN document R1-092634, entitled “CoMP Operation Based on Spatial Covariance Feedback and Performance Results of Coordinated SU/MU Beamforming,” Los Angeles, Calif., Jun. 29-Jul. 3, 2009, which is incorporated herein by reference.
3GPP TSG RAN document R1-093474, entitled “Coordinated Beamforming with DL MU-MIMO,” Shenzhen, China, Aug. 24-28, 2009, which is incorporated herein by reference, describes a Multi-User MIMO (MU-MIMO) scheme with coordinated beamforming, which is based on a long-term wideband transmit covariance matrix.
CoMP schemes are also considered for LTE-Advanced (LTE-A) systems. Example CoMP schemes for LTE-A, with reference to feedback, are described in 3GPP TSG RAN document R1-093833, entitled “System Performance Comparisons of Several DL CoMP schemes,” Miyazaki, Japan, Oct. 12-16, 2009, which is incorporated herein by reference. 3GPP TSG RAN document R1-093132, entitled “DL performance of LTE-A: FDD,” Shenzhen, China, Aug. 24-28, 2009, which is incorporated herein by reference, describes LTE-A MU-MIMO schemes with CoMP using Frequency Division Duplexing (FDD). 3GPP TSG RAN document R1-093109, entitled “Feedback in Support of DL CoMP: General Views,” Shenzhen, China, Aug. 24-28, 2009, which is incorporated herein by reference, discusses several feedback design options for implementing CoMP in LTE-A systems.